1. Technical Field of the Invention
The present invention relates to novel topically applicable aqueous cosmetic compositions for the photoprotection of human keratin substrates, such as the skin, against the deleterious effects of ultraviolet radiation (these compositions hereinafter more simply designated "antisun" or "sunscreen" compositions).
This invention more specifically relates to the aforesaid sunscreen/cometic compositions comprising at least one UV-screening active agent, a dispersion of non-film-forming polymer particles having a specific refractive index and a fatty phase also having a specific refractive index, and to the use of same for those applications indicated above.
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths of from 320 to 400 nm (UV-A) promotes tanning of the human epidermis; however, this radiation also causes damage to the epidermis, especially in the case of pale skin or a skin which is sensitive to UV, or in the case of skin which is continuously exposed to solar radiation. U-VA, in particular, causes a loss in the elasticity of the skin and the appearance of wrinkles, promoting premature aging thereof.
It is also known to this art that light radiation of wavelengths of from 280 to 320 nm (U-VB) causes skin burns and erythema which may, via inflamation, effect a certain level of aging of the skin. It is thus necessary, in order to conserve proper skin quality after exposure to UV radiation, to protect the skin during this exposure.
A wide variety of cosmetic compositions/compounds for the photoprotection of keratin substrates and substances, and in particular the skin, are known to this art. Exemplary thereof are, for example, hydrophilic or lipophilic aromatic compounds capable of absorbing in a wavelength range in the region 280-315 nm and/or in the region 315-400 nm. Sunscreen/antisun cosmetic compositions comprising nanoparticles of inorganic oxides which are capable of absorbing and/or reflecting UV are also known.
The efficacy of a sunscreen composition for photoprotecting the skin is generally reflected in terms of its sun protection factor (SPF), which is defined by the ratio of the amount of energy required to initiate erythema on skin protected by the agent for screening UV radiation to the amount of energy required to initiate erythema on unprotected skin.
Certain active species exhibiting UV-radiation-screening properties and incorporated into sunscreen formulations are potentially toxic vis-a-vis the skin or other human keratin substrates. It is generally sought to lower the risks of toxicity by reducing the amount of UV screening agent in the sunscreen formulations, while at the same time conserving the SPF level of protection against the damaging effects of UV radiation.
EP-A-681,830 describes such objective, via combining, with organic systems for screening out UV radiation, a mixture of polymers including an ethylene/vinyl acetate copolymer and an acrylic polymer in the form of particles, such as to increase the sun protection factor (SPF) thereof.
EP-A-669,124 also describes such objective by formulating a sunscreen composition comprising a combination of an organic system for screening out UV radiation and a latex of hollow particles of crosslinked polymer in dispersion.